Preheat your oven to 350°F (175°C) and grease the 9x13 inch cake pan with butter or non-stick spray.
In a mixing bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt. Set aside.
In another large mixing bowl, cream together the softened butter and granulated sugar using an electric mixer until light and fluffy, about 3-4 minutes.
Add the eggs, one at a time, beating well after each addition. Mix in the vanilla extract, lemon zest, and lemon juice until well combined.
Gradually add the flour mixture to the wet ingredients, alternating with the buttermilk. Begin and end with the flour mixture. Mix until just combined; do not overmix.
Gently fold in the fresh blueberries with a rubber spatula, being careful not to break them.
Pour the batter into the prepared cake pan, smoothing the top with a spatula. Bake in the preheated oven for 30 minutes, or until a toothpick inserted into the center comes out clean.
Once baked, remove from the oven and allow the cake to cool in the pan for 10 minutes. Then transfer it to a cooling rack to cool completely.
Serve as is or dust with powdered sugar or a simple lemon glaze, if desired.